PRACTICAL ORGANIC CHEMISTRY
PREPARATIONS Si — 82.
Phenolphthaleiii. — The action of phthalic anhydride on
phenol takes place in two ways. When equal molecules of the
substance react in presence of cone, sulphuric acid, hydroxyan-
thraquinone is formed (Baeyer),
= C(1H4< >C0IT.,OH + 11,0.
It is by a similar process that alizarin has been synthesised
with the object of ascertaining its constitution (see Notes on
Prep. 1 10, p. 316), When two molecules of phenol and one mole-
cule of phthalic anhydride are heated together with cone, sul-
phuric acid, then phenolphfhalein is formed (Baeyer). Its
constitution has been determined by its synthesis from phthalyl
chloride and benzene by means of the " Friedel-Crafts3 reaction"
(see Notes on Prep. 100, p. 309), Phthalyl chloride and benzene
yield in presence of A1C13 phthalophenone,
Phthalophenone is then converted successively into dinitro-,
diamino-, and, finally, by the action of nitrous acid, into clihydr-
oxyphthalophenone or phenolphthalein,
r^C(;U, r C6H4N0.2
Mi1 M \/
An important group of colouring matters, known as the
" rhodamines," is obtained from phthalic anhydride and m-
aminophenol and its derivatives. They have a constitution similar